Effects of sea-water acidification on fertilization and larval development of the oyster Crassostrea gigas

Oceans face a serious change to their natural biogeochemical cycle due to the rapid absorption of CO2 generated by human activities. Ocean acidification is the common term used to describe the decrease of seawater pH caused by the absorption of atmospheric CO2. To evaluate the effects of ocean acidification, we focused on the larval stage of bivalves, which produce a fragile calcareous skeletal structure, very sensitive to changes in seawater chemistry. In this context, we investigated sperm motility, fertilization rate and larval viability (survival, growth and abnormalities) of the Pacific oyster, Crassostrea gigas, a commercially important bivalve, in a controlled CO2 perturbation experiment. The carbonate chemistry of seawater was manipulated by diffusing pure CO2, to attain two reduced pH levels (ΔpH = − 0.4 and ΔpH = − 0.7) which were compared to unmanipulated seawater. The results show high sensitivity of C. gigas veliger larvae to low values of pH, as reflected by a decrease in survival and growth rates, as well as an increased frequency of prodissoconch abnormalities and protruding mantle. Moreover, results also show that sperm motility, fertilization rate, and hatching success, were negatively influenced by acidification. The exposure to ΔpH = − 0.7 had a higher impact on the fertilization and larval viability than ΔpH = − 0.4. The results suggest that the reproductive success and the biological mechanisms for calcification may be prematurely interrupted and disturbed when C. gigas veliger larvae are exposed to an acidified environment which may reduce their viability and compromise settlement and future abundances of this species.